Alternator/Battery Help (1 Viewer)

[ymudd]

First time posting in Vehicle Tech, really appreciative of all the existing how-to's, thanks for all the contributors to this super handy site.

Short version: Replaced my '99 battery and alternator this weekend following several 'mud how-to's. Now my battery voltage is jumping *up* from baseline, usually after 8-10 minutes of driving, causing the battery dash light to flash. What did I do wrong?

Longer version: First time doing any substantial work on the cruiser. Cruiser died while wife was out driving, a mobile tech replaced the battery and said the alternator was bad. Both make sense: battery (Costco) was about at the end of its life here in Arizona (~3.5 yr). And I'd been hearing a high-pitched whine that in retrospect was probably the alternator. Also, had a power steering leak recently.

• Removed unit was NOT original, so I just replaced. Replacement unit is also not OEM.
• I wasn't sure what the amperage was on previous unit, so I got a 100 amp.
• I did not replace the connector plug, although existing one is pretty beat up. It seemed snug enough, although it doesn't 'click' in.
• I had to unthread the tensioner pulley quite a bit to pull the alternator, because it obstructed removing sliding the alternator off the upper alternator mount. I didn't have to remove it though, and just tightened it back up after replacing alternator.
• Using Torque Lite, Volt Gauge for OBD Adaptor reads a steady voltage (usually 13V, sometimes 12.x) when I start the car and at idle. Dash gauge stays steady 1 tick below 18V.
• After 8-10 minutes of driving, dash needle will sporadically rise in the direction of 18V and battery light flashes. TorqueLight gauge shows jumps to 15 - 16.5V. At that point I ease up and bring the car to a crawl.
• Turning on AC or accelerating into turns seems to make it worse, although not within the first 5-10 minutes of driving.
• I checked/tightened the battery terminals and both the ground (10mm nut) and the connector on the alternator, no effect.
• I checked the fuses under the hood.

Current ideas:

1. As a complete novice, I selected the wrong alternator
2. I bought an alternator with a faulty voltage regulator
3. I need to replace the alternator connector plug, or somehow otherwise damaged the old wiring and didn't notice
4. I somehow messed up the tension pulley when I unthreaded it, hence the 5-10 minute safe period, and erratic changes when engaging AC, etc.

Completely new to electrical, so any help appreciated. Thanks!

 

[loganbrew]

I need to replace the alternator connector plug, or somehow otherwise damaged the old wiring and didn't notice

Ensure the connection is good first. And clean. At those miles there's likely plenty of gunk in the area from power steering or steering rack leaks.

One of the wires to that connector is a "sense" wire. It goes direct to the battery, which the voltage regulator (within the alternator) uses as an input to regulate the voltage to the battery. If the sense connection is bad you might see the erratic voltages you describe.

 

[ymudd]

Thanks Logan, that makes sense. It sounds like the next troubleshooting step is to install a new connector then.

I was (wishfully) thinking I might be able to replace the connector plug without yanking the alternator again. When originally troubleshooting, I was able to tighten the alternator ground and get a visual/feel on the connector from the passenger side, without removing anything.

Any info out there on replacing the connector from above with alternator still in place? Or maybe I'll just have to pull it all apart again next weekend...

 

[loganbrew]

You can remove the entire cable without removing the alternator. You might just pull it out far enough away from the alternator (up and towards radiator) to inspect. But don't forget to completely disconnect the battery ground terminal first!

 

[ymudd]

Awesome, great to hear. Thanks! Ordered the connector, we'll see if that fixes it.

 

[loganbrew]

Cool. Hint: give likes, they count here

 

[ymudd]

Haha, I had no idea. done!

 

[Dox]

Haha, I had no idea. done!

Any update? I have a voltage spike after replacing my alternator with a Denso one.

 

[fjcruising]

Any update? I have a voltage spike after replacing my alternator with a Denso one.

Mine did this after replacing it, but after 10k miles I forgot about it and noticed it doesn’t do it anymore (I was blaming it on the aftermarket replacement I should have never gotten but thought I’d be cheap for the weekend). I wonder if they settle in after time…

 

[ymudd]

Hey guys,

Apologies for not following up. I'm in the process of moving, which kind of delayed addressing this issue.

So, mine actually got worse over time. It would run fine for 10-15 minutes, and then the voltage spiking would happen.

I replaced the pigtail, which didn't help. The local place where I got the alternator couldn't find a problem with the alternator either.

I ultimately took it to a local auto electric place recently, who tested the alternator and found it was faulty. Took the alternator from them back to the alternator shop, which still said it tested fine, and they're a pretty reputable local shop. Even though they couldn't find an issue, they swapped me a replacement unit. That unit is working fine so far. Fingers crossed the problem is solved.